The present invention relates to a novel electrode arrangement and method for an automatic implantable cardioverter/defibrillator. The electrode arrangement includes a catheter electrode intravenously positioned within the heart of a patient wherein one electrode on the catheter is within the right ventricle and a second electrode on the catheter is within the superior vena cava. A third electrode, in the form of a flexible, substantially planar patch, is subcutaneously positioned outside the thoracic cavity proximate to the apex of the left ventricle. The third electrode is electrically connected with the second electrode of the catheter.
Approximately 250,000 Americans under the age of 65 die yearly from a condition termed "sudden cardiac death". In the vast majority of these cases, the cause of death is ventricular tachycardia and/or ventricular fibrillation. An automatic implantable cardioverting/defibrillating device has been developed and shown to be effective in preventing sudden cardiac death from these causes. See, for example, U.S. Pat. No. 4,407,288
As used herein, the term cardioversion may be generally defined as the correction of either ventricular tachycardia or ventricular fibrillation by the discharge of electrical energy into the heart (0.1-40 joules when discharged through internal electrodes). Ventricular tachycardia is an abnormally rapid heart rate (120-180 beats per minute) originating in the the heart's main pumping chambers (ventricles) which is regular in periodicity and oftentimes is life threatening to the patient. Ventricular fibrillation is generally a more rapid heartbeat disorder, disorganized and irregular, or non-periodic, and is fatal unless corrected within minutes by the discharge of electrical energy through the heart. More specific medical terminology often uses the term cardioversion to mean the synchronized delivery of an electrical shock to the heart to correct ventricular tachycardia. Defibrillation, then, is often referred to as the nonsynchronized delivery of electrical energy to the heart to correct ventricular fibrillation. Internal cardioversion is usually effective with 0.1 to 3 joules of electrical energy when delivered in synchronism with the electrical heartbeat. Internal defibrillation requires 5 to 30 or more joules of electrical energy, depending largely on the electrode system used.
Over the years, a number of different types of electrode systems have been suggested for use with an automatic implantable cardioverter/defibrillator. For example, U.S. Pat. No. Re. 27,757 describes an electrode arrangement whereby one electrode is formed on the distal end of an intravascular catheter that is positioned within the right ventricle, whereas the second electrode is positioned on the surface of the chest or sutured under the skin of the chest wall or directly to the ventricular myocardium. U.S. Pat. No. 3,942,536 discloses a catheter electrode system wherein both electrodes are on a single intravascular catheter. The distal electrode is wedged in the apex of the right ventricle and the proximal electrode is immediately superior to the right atrium.
An improved intravascular catheter electrode system is described in copending U.S. Pat. No. 4,603,705 filed on May 4, 1984, issued on Aug. 5, 1986 and assigned to the same assignee as the present invention. There, the proximal electrode is located in the superior vena cava and the distal electrode is in the right ventricle. A sensing and pacing electrode is also provided at the distal tip of the catheter. The first two electrodes constitute the anode and cathode of the cardioverting/defibrillating electrode pair. The tip electrode is used for sensing heart rate and pacing the heart. Using this single catheter system, energies required to defibrillate the human heart have been found to vary between 5-40 joules, but in some 40-50% of patients, even the higher energies may be insufficient to defibrillate the heart. Thus, although this improved catheter electrode system has many advantages, such as the capability of being installed without surgically invading the thoracic cavity, it has been found to have somewhat limited effectiveness in terminating ventricular fibrillation.
Various other electrode arrangements have also been employed. In U.S. Pat. No. 4,030,509, the implantable electrode system includes, among others, a flexible apex electrode designed to surround the apex of the heart, and various flexible base electrodes designed to surround the base of the heart.
The electrodes presently used by the automatic implantable cardioverter/defibrillator consist of one defibrillating electrode placed in the superior vena cava/right atrial region, and a second flexible, conformal, defibrillating electrode placed on the outside of the heart, typically over the lateral wall of the left ventricle. See, U.S. Pat. Nos. 4,161,952 and 4,270,549. Placement of the first electrode can be accomplished by the insertion of a catheter-mounted electrode into one of the veins outside of the thorax and sliding the catheter electrode centrally into the venous system until the electrode portion is within the thorax and located at the junction of the superior vena cava and right atrium. Thus, for the placement of this electrode, it is not necessary to surgically enter the thorax. For the second electrode, however, it is necessary to make one of a variety of surgical incisions to open the thoracic cavity in order to place the electrode over the left ventricle of the heart. Each of these surgical approaches has serious disadvantages. Two such approaches involve extensive surgery and substantial patient recovery time with a cost currently between $8-12,000. These approaches consist of splitting the sternum (breastbone) or alternatively opening a space between the ribs in order to gain access to the surface of the heart. A third approach involves making a smaller incision under the xiphoid process of the sternum, which is simpler from a surgical point of view, but still involves entering the thoracic cavity. Moreover, this approach sometimes does not allow convenient positioning of the left ventricular electrode.
With providers of health care becoming increasingly cost conscious due to limited payment resources, it is more and more important to reduce surgical costs in order that life-saving therapies can be made broadly available. Thus, to both reduce the morbidity associated with the surgery of defibrillator electrode implantation and to reduce the cost, it is highly desirable to have a means of electrode implantation which does not involve the surgical opening of the thoracic cavity.